1. Field of the Invention
This invention relates to a brushless DC motor having a magnet (field flux generating means) and multiphase coils, and more particularly to a brushless DC motor in which a current is distributed from a DC voltage source to said multiphase coils by selectively activating two sets of output transistors, according to the relative position between said magnet and said multiphase coils.
2. Description of the Prior Art
According to the prior art, in a brushless DC motor Y-connected multiphase coils are supplied with bidirectional currents by full-wave signals. The terminal of each coil of the multiphase coils opposite to the common terminal of the Y connection is each connected to one current supplying means through one set of output transistors (first output transistors) and also each connected to the other current supplying means through the other set of output transistors (second output transistors). By designing the two sets of output transistors to operate differentially, the two sets of output transistors can selectively cause a current to flow through the common terminal of the Y connection time sequentially.
Such a brushless DC motor is theoretically capable of keeping the selectively-and-sequentially-flowing current constant, avoiding the current flow through unselected coils and switching the current flow through the coils precisely. However, this theoretical operation occasionally cannot be achieved in practice due to the difference between the current commanded by one current supplying means and the current commanded by the other current supplying means. Thus, the characteristics of the motor operation are deteriorated by the undesired flow of currents to the multiphase coils.
The U.S. Pat. No. 4,035,700 discloses an electronic control apparatus for a brushless DC motor, which overcomes the defects described hereinbefore by detecting a voltage at the common terminal of the Y-connected multiphase coils and controlling a current supplied to the multiphase coils through one set of output transistors so that the voltage at the common terminal is equal to a reference voltage. Though this apparatus described in U.S. Pat. No. 4,035,700 has many excellent characteristics for a brushless DC motor, it is necessary for the common terminal of the Y-connected multiphase coils to be picked up from the motor structure and to be connected to an electronic control circuit only for detecting the voltage at the common terminal. This increases connecting lines between the motor structure and the control circuit, which is disadvantageous for mass production.
Furthermore, it can be used only for a brushless DC motor having Y-connected multiphase coils, in other words, it cannot be used for a brushless DC motor having delta-connected multiphase coils.